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Glassed in chainplates

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I have a 34' Pilothouse. Deck stepped mast of about 43' from deck level. The chainplates, backstay and forestay attachments are all glassed in stainless T shaped pieces. No weeping or signs of corrosion.

 

I know this is used in other boats successfully but I want to use this as a retirement, coastal cruiser. I searched the forum (as best you can anymore) and couldn't find a specific discussion. So how safe is this style of construction??

 

Any input from the wise and all knowing SA'ers would be appreciated. On second thought, I would settle for most anyone's opinion :P :P

 

WL

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I fI understand the construction you are referring to, it is a very safe construction - for those chainplates to fail , it would have to take half your hull and deck with it - and if that goes , you're probably not too worried about your rig performance.

 

Pics are always great (especially of breasts .. preferably human)

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I have a 34' Pilothouse. Deck stepped mast of about 43' from deck level. The chainplates, backstay and forestay attachments are all glassed in stainless T shaped pieces. No weeping or signs of corrosion.

 

I know this is used in other boats successfully but I want to use this as a retirement, coastal cruiser. I searched the forum (as best you can anymore) and couldn't find a specific discussion. So how safe is this style of construction??

 

Any input from the wise and all knowing SA'ers would be appreciated. On second thought, I would settle for most anyone's opinion :P :P

 

WL

The concern is whether there is any moisture in there. If there is there could be well hidden stainless corrosion. It's damn hard to know . . .but I am told that you can tell something with an IR photo

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If they used 316 stainless it should be ok

If they used 304 stainless and water gets in you could have a problem.

I have seen 304 chain plates on dinghies corrode out where they go through a deck.

The water gets trapped with no oxygen and the 304 stainless corrodes, eventually a failure.

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Alex-

 

That link was great. Thank you for that!

 

Gouv- I am not familiar with the technique you are describing? Could you give a little more detail? Thanks

 

WL

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I strongly recommend you read the thread on buried chains on SailNet - after you see what came out from under the glass on that big Irwin, I doubt you will be satisfied with anything but cutting them out and replacing with proper exposed chains.

 

A critical level of crevice corrosion on S/S can be almost invisible from the surface - ask me how I know.

 

Scanning or X-raying it in situ seems to be of very limited effectiveness.

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If they used 316 stainless it should be ok

If they used 304 stainless and water gets in you could have a problem.

I have seen 304 chain plates on dinghies corrode out where they go through a deck.

The water gets trapped with no oxygen and the 304 stainless corrodes, eventually a failure.

2205 beats 316 (0.02% yield) hands down. UTS is about double and with superior corrosion resistance. Also comes with heat sheets.

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Go to www.iphomeport.com and do a search on chain plates. There's a wealth of info there, both on replacement and maintenance. Island Packets all have glasses in chain plates and the topic has been discussed in depth.

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The fact that IP's use them is not a vote FOR them, it is a strike against IP's.

 

Glassed in chains have only one virtue - they are cheap & easy to install.

 

That's it - everything else about them sucks, especially redoing them into a quality installation.

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I wasn't making a judgement for or against but simply pointing the OP to a site where the subject has been discussed in depth.

 

Discussing all things for / against IPs is best done over a bunch of beers / rum drinks, me thinks

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^^ the IP's are held in place with fans of uni glassed to the hull.

 

post-37611-0-10930500-1390926196_thumb.jpg

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tks.... and yuk...

 

friend of mine's oday yingling had U shaped chain plates with the top of the U of course above deck. the bottom portion was glassed in with a piece of wood going through the bottom of the U.. well enough water seeped between the chain plate tops and the deck that the wood pieces rotted to hell.. needless to say, the mast didn't stay upright

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That IP design looks quite strong and redundant, if difficult to inspect. The likeliest spot for crevice problems is where the chainplate passes thru the teak cap rail. Wood moves, and it retains moisture in itself Tough to keep water away from the plates there.

 

Many older boats simply used T-shaped steel plates, with the crosspiece sandwiched between layers of mat, fabric, and polyester resin. Seems kinda dodgy, as tension in the rigging would act parallel to glass layers, but many are still out there and going strong. Our San Juan 21 is made that way -- shrouds and backstay. No thru bolts at all. Forty two years and counting....

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There are well proven designs for "glassed in" carbon chainplates, that have none of the corrosion concerns/problems that stainless ones have. I would suggest carbon is the better solution if you want to make (or replace) one of the integral chainplate systems.

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Glassed in s.s. strap chainplates would scare the crap out of me, 316 or not. I would EXPECT corrosion where it passes through the deck.

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Seems like a good place for titanium, also. CF is amazing stuff, but its yield strength and ultimate strength are pretty much identical, aren't they? Given the historical difficulty engineering for transient rig loads, there may be some value in a chainplate that deforms before rupture. Metal in a marine environment = headaches always, but I do like me some ductility at Strainmax.;)

 

You often see photos of deformed metals: elongated clevis holes, or a bent tang, or maybe a bolt that has a dogleg in its shank. Holy cow, the owner says (or you say) -- glad I caught that before the whole rig came down! Obviously the part had been subjected to some load greater than the designer anticipated, or a load from an unanticipated direction. The part is compromised, but it held out long enough for someone to find it.

 

Metal is handy that way.:)

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True - but when I did the calcs for the CF chain plates ony boat the required thickness was something like 2.2 mm (including the safety factor). So I made them about 8 mm so my wouldn't think they were too thin. Huge SF and I sleep well at night

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^^ exactly, you can easily just build in huge safety factors with CF.

 

There are lots of CF rudder shaft breakage cases, but I am not aware of any CF chain plate failure - there must be some cases somewhere, but practically/empirically speaking it seems like a much 'easier' application than rudder shafts.

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^^ Bob, that may well be true . . .I don't have any decent data going back that long . . . but new carbon rudder shafts are still breaking at a decent clip (a couple a year) . . .just as the most public examples see the UU incident, and one in the return from the last bermuda race.

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I have an 18 year history with engineering carbon stocks and have only one failure. That as best as we figured out was initiated by someone torching off a bearing sleeve when they changed bearings.

 

I of course don't have data on other peoples work, but one thought that keeps cropping up is that some may be trying to use HM carbon. When I ran the progressive ply failure study for HM, it seemed like all the plies failed within a very small margin so I decided it was a bad idea. Both HS and IM carbon perform quite well, but it takes good workmanship and good QA to make sure the product is what it is supposed to be.

 

We've had great success with composite chainplates, but since people tend to abuse chainplates by tying spring lines to them, I don't suggest them on cruising boats. As far as glassing in metal chainplates, there should be little worry as far as separating the GRP over time. Corrosion may be another issue, but I have seen them last over 30 years. It is certainly not a worse way of attachment than bolting to plywood bulkheads.

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If the hull were carbon, I would stay with carbon chainplates. I have done E-glass chainplates on several of Mills custom boats like Tiamat / Cool Breeze, Mariner's Cove, Thunder etc. I'd do S-glass chainplates only on an S-Glass build and there are not too many of those. For production builds, I stay with 316L SS chainplates either bolted through the hull or sheer, or else to GRP bulkheads. Occasionally we do glassed in forestay chainplates when there is a below deck furling unit and the forestay is some distance back from the stem.

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More practicality than anything else. In the past 5-6 years, distributors and manufacturers have reduced inventories and don't stock or even make specialty fabrics unless you are going to order a pallet. Chainplates use a small amount of UDR and UDR is used in stringer, bulkhead, and floor capping so why not use the same thing for chainplates? One of the first conversations I have with a builder is about what skin weights we are trying to achieve VS what materials they can readily obtain in their corner of the world.

 

For the most part, boat engineering is concerned with stiffness as much and sometimes more than ultimate strength. S-glass is stronger, but there is little gain in stiffness so there are few places in boats that it is worth using. It you can find S-glass, the only thing usually available is 200 GSM UDR or 400 GSM +/- 45. There are good gains in stiffness with carbon but it is pointless to use carbon with polyester and not ideal with VE. Also with Carbon, the difference in modulus as opposed to E-glass means that whatever carbon gets used had better handle all the forces on its own. The- E-glass won't get loaded up until after the carbon fails.

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Foxxy - you sound extremely knowledgeable - what is your background in this stuff? Not being a smartass, I'd really like to know.

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I guess there are two different design 'philosophies' displayed in this thread.

 

(1) Glassed in stainless chain plates may last 20-30 years, so it is good (or at least adequate) design

(2) Designing a critical structural component so that it has a known failure mode than is not inspect-able or reparable without cutting the boat apart = bad design, especially when there are certainly better techniques available.

 

I guess I lean toward camp 2. Camp 1 is often ok for the first owner, but a pain in the ass for a later owner.

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Estar - you nailed it.

 

Glassed in chains are quick & dirty - period. They take a major amount of work to correct - removing cabinetry, cutting & grinding glass (inside :o ), creating a proper mounting system etc.

 

They suck in every way possible except saving the builder money.

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Foxxy - you sound extremely knowledgeable - what is your background in this stuff? Not being a smartass, I'd really like to know.

Been building and engineering boats professionally for over 40 years & started building my own boats at 13. Everything from cold molded wood boats to custom composite race boats, to production boats, Even a few powerboats from time to time.

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I guess there are two different design 'philosophies' displayed in this thread.

 

(1) Glassed in stainless chain plates may last 20-30 years, so it is good (or at least adequate) design

(2) Designing a critical structural component so that it has a known failure mode than is not inspect-able or reparable without cutting the boat apart = bad design, especially when there are certainly better techniques available.

 

I guess I lean toward camp 2. Camp 1 is often ok for the first owner, but a pain in the ass for a later owner.

 

You could make the same arguments for SS rudder stocks. You take a welded chunk of metal, encase it in foam and fiberglass where you can't inspect it and stick it under sea water for 20-30 years. The truth is that every boat has some compromises be it for cost, accommodations or purpose. You either accept that compromise for what it is or you pass up the boat.

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^^ Yes, every boat is a mess of compromises. The question is always whether there is some much better alternative available.

 

For chain plates there is and always have been better techniques than embedded stainless in fiberglass..

 

For rudder stocks, stainless was hard to beat 30 years ago. And there is still a valid argument/debate that, because of UFO's, its ability to bend is a better failure mode than carbon. I have an all aluminum rudder (stock, frames and skin), which has its own compromise/failure mode (electrolysis), but it is at least inspect-able for that.

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